Is our sense of fairness genetic?

An international team of researchers including an MIT graduate student has demonstrated for the first time that genes exert influence on people's behavior in a very common experimental economic game.

Traditionally, social scientists have been quite hesitant to acknowledge a role for genes in explaining economic behavior. But a study by David Cesarini, a Ph.D. student in MIT's Department of Economics, and by colleagues in Sweden indicates that there is a genetic component to people's perception of what is fair and what is unfair.

The paper, published in the Oct. 1 advanced online issue of the Proceedings of the National Academy of Sciences, looked at the ultimatum game, in which a proposer makes an offer to a responder on how to divide a sum of money. This offer is an ultimatum; if the responder rejects it, both parties receive nothing.

Because rejections in the game entail a zero payoff for both parties, theories of narrow self-interest predict that any positive amount will be accepted by a responder. The intriguing finding in the laboratory is that responders routinely reject free money, presumably in order to punish proposers for offers perceived as unfair.

To study genetic influence in the game, Cesarini and colleagues took the unusual step of recruiting twins from the Swedish Twin Registry, and had them play the game under controlled circumstances. Because identical twins share the same genes but fraternal twins do not, the researchers were able to detect genetic influences by comparing the similarity with which identical and fraternal twins played the game.

The researchers' findings suggest that genetic influences account for as much as 40 percent of the variation in how people respond to unfair offers. In other words, identical twins were more likely to play with the same strategy than fraternal twins.

Meanwhile, over at his blog, George Borjas points us to a related article about chimps playing the ultimatum game:

German researchers have demonstrated chimpanzees make choices that protect their self-interest more consistently than do humans.Researchers from the Max Planck Institute of Evolutionary Anthropology in Leipzig studied the chimp's choices by using an economic game with two players.

In the game, a human or chimpanzee who receives something of value can offer to share it with another.If the proposed share is rejected, neither player gets anything.Humans typically make offers close to 50 percent of the reward. They also reject as unfair offers of significantly less than half of the reward, even though this choice means they get nothing.

The study, however, showed chimpanzees reliably made offers of substantially less than 50 percent, and accepted offers of any size, no matter how small. The researchers concluded chimpanzees do not show a willingness to make fair offers and reject unfair ones. In this way, they protect their self interest and are unwilling to pay a cost to punish someone they perceive as unfair.

The study appeared in the Oct. 5 issue of the journal Science.

The sense of fairness demonstrated by the ultimatum game is apparently genetic and intrinsically human.

About Me

I am the Robert M. Beren Professor of Economics at Harvard University, where I teach introductory economics (ec 10). I use this blog to keep in touch with my current and former students. Teachers and students at other schools, as well as others interested in economic issues, are welcome to use this resource.